Standing nearly four metres tall and weighing around six tonnes, the largest animal living on land – the African bush elephant – is a pipsqueak compared to some of the creatures in the ocean. With the water to support their weight, marine animals can reach epic sizes.
There are lots of behemoths in our seas, including the largest animal on the planet: the blue whale. Which titans we include in the rest of the list of biggest ocean creatures can depend on several factors: are we measuring by length or weight? Do we include colonial animals? Can we be sure that some historical records are accurate?
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And, of course, there are still so many mysteries when it comes to the underwater world, including species yet to be discovered or variety within individual species. With that said, here are a few of our favourite ocean giants.
Biggest animals in the ocean
Blue whale
Reaching an epic 30 metres in length, and weighing around 160 tonnes, blue whales are not only the largest animals in the sea but also the biggest creature on the planet.
Despite their enormous size, they feed on tiny shrimp-like organisms called krill. They do this by taking huge gulps of water and straining out the krill that is caught in their mouth. To get enough energy to support their massive size, they need to gorge themselves on as many as 40 million krill each day.
Fin whale
The second largest whale on the planet typically gets much less attention, despite being just a few metres shorter than the blue whale. The maximum length of a fin whale is believed to be around 27 metres. These huge baleen whales can be found in all the world’s oceans but prefer cooler waters so aren’t typically seen in the tropics.
- Fin whale guide: how big they are, their lifespan - and just how fast they can swim
- How do baleen whales eat so much when they don't have teeth?
Right whale
Once targeted by whalers, these animals got their name because they were seen as the “right whales” to hunt. They swam slowly, making them easy to kill, and floated once they were dead so the whalers could recover the carcass.
Growing to around 18.5m, they are also among the biggest animals in the sea. But they are under threat. There are fewer than 400 North Atlantic right whales alive today, and conservationists are worried that the population could be lost forever.
Sperm whale
Although several other baleen whales are larger, a special shout out goes to one of the most fascinating whale species. Sperm whales are the biggest of all the toothed whales and are believed to have inspired the tales of legendary sea monsters including Moby Dick and Jonah and the Whale. Measuring up to around 20m (although typically more like 16m), sperm whales are so big that they are often grouped together with the great whales.
Whale shark
When it comes to fish, the biggest is the enormous whale shark (the “whale” in their name comes from their huge size). These beautiful, gentle sharks feed on plankton and are recognisable by the smattering of white dots which look like a constellation of stars on their dark backs.
Juveniles are seen much more often than adults but researchers believe that females (which get larger than males) measure between 12 and 14.5 metres on average. The largest whale shark ever (reliably) recorded was longer than a ten-pin bowling lane, at 18.8m. Others have reported seeing 20 metre-long individuals but their claims haven’t been verified.
Giant squid
The rarely seen giant squid looks so alien that it’s not surprising that sightings of this creature inspired the myth of the Kraken – a terrifying monster that sank ships and sent sailors to a watery grave.
With tentacles that can stretch for 13m, these animals are the longest invertebrates on Earth. But, when judging by weight, another huge squid wins the prize for biggest invertebrate. The colossal squid is shorter (up to around 5m) but much heavier.
While the heaviest giant squid on record tipped the scales at 220 kilograms, the heaviest colossal squid was around 495kg.
Coral
For some ocean animals, community living is the way forward. Coral polyps are tiny animals that come together to form colonies (and several colonies make up the colourful coral reefs we know and love). These coral colonies can be vast. The largest on record, which was found near the Solomon Islands in the Pacific Ocean measures a staggering 34m wide and 32m long. Experts believe that this mega coral, which can be seen from space, is around 300 years old.
Long stringy stingy thingy
Another immense colonial creature is the wonderfully named long stringy stingy thingy (yes, that’s actually its name). According to the Guinness Book of Records, this colonial siphonophore typically measures up to three metres long. But much longer examples have been found. In 2020, a gigantic 119m colony was spotted off the coast of Western Australia – making this the longest free-living colonial animal not just in the ocean but in the world.
Nomura’s jellyfish
The biggest jellyfish in the world is often said to be the magnificent Lion’s mane jellyfish, named for its bushy red tentacles which resemble the king of the jungle’s coat. However, this is based on a report of a 37-metre-long individual which was caught off the coast of North America in 1856. But some say this is a tall tale and think the Nomura's jellyfish,with its six-metre tentacles, is more likely to win the crown for the largest jelly.
Japanese spider crab
Crustaceans may not grow as big as some other underwater creatures but the largest marine crustacean is worth a mention in our list of impressive beasts. With its leg span of 3.69m (longer than a king sized bed), the Japanese spider crab is the stuff of nightmares. However, despite being the longest marine crustacean, the American lobster is even heavier.
